Over 100 million tons of ammonia is produced per annum using about 2% of the world's energy consumption. Ammonia is used mainly in the fertiliser industry (>80%) and for industrial processes (20%) as a source of nitrogen. Ammonia is produced at present through the Haber-Bosch process, which is an energy intensive process requiring hydrogen and nitrogen to react (i.e. 3H2+N2→2NH3) on an iron based catalyst at high temperatures (up to 500° C.) and high pressure (up to 300 bar). This reaction is exothermic and has a negative entropy change that requires high temperatures (kinetics) and high pressures for the reaction to proceed at reasonable rates, and there is only 10-15% conversion of reactants at each stage. Consequently, the step is repeated a number of times. The total energy consumption by this route is very high at 9500 kwh/ton of ammonia produced (12000 kwh/ton if H2 is produced via electrolysis rather than via natural gas reforming).
Other methods of producing ammonia include electrochemical based processes. The electrochemical route for production of ammonia can save more than 20% of the energy consumed as compared to the Haber-Bosch process, although still requires relatively high energy input and also suffers from low conversion rates. Hydrogen can be sourced from natural gas reforming or electrolysis of water, or can be produced in situ by electrolysis of water or decomposition of an organic solvent such as ethanol. The process can be carried out under ambient conditions or at higher temperatures depending on the type of the electrolyte material used.
There is a need to find an alternative route for ammonia synthesis that can reduce the severity of the process conditions, lower the energy consumption per unit of ammonia produced, and enhance the ammonia conversion rates.
Other industrially important chemical processes include hydrogen peroxide synthesis from oxygen and hydrogen, and hydrocarbon synthesis from carbon monoxide or carbon dioxide and hydrogen. Such processes either involve catalysed reactions operating at high temperatures and pressures, or direct or indirect electrochemical processes that also require a high energy input.
The above industrial processes are extremely energy intensive have low efficiency and energy recycling is poor. There is thus a need to identify novel processes for large scale synthesis of products at reduced energy inputs.